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parser.go
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parser.go
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// Package stagparser provides a generic parser for golang struct tag.
// stagparser can parse tags like the following:
//
// * `validate:"required,length(min=1, max=10)"`
// * `validate:"max=10,list=[apple,'star fruits']"`
//
// tags are consists of 'definition'. 'definition' have 3 forms:
//
// * name only: required
// * name with a single attribute: max=10
// * in this case, parse result is name="max", attributes={"max":10}
// * name with multiple attributes: length(min=1, max=10)
//
// name and attribute must be a golang identifier.
// An attribute value must be one of an int64, a float64, an identifier,
// a string quoted by "'" and an array.
//
// * int64: 123
// * float64: 111.12
// * string: 'ab\tc'
// * identifiers are interpreted as string in value context
// * array: [1, 2, aaa]
//
// You can parse objects just call ParseStruct:
//
// import "github.com/yuin/stagparser"
//
// type User struct {
// Name string `validate:"required,length(min=4,max=10)"`
// }
//
// func main() {
// user := &User{"bob"}
// definitions, err := stagparser.ParseStruct(user)
// }
package stagparser
import (
"bytes"
"fmt"
"reflect"
"strconv"
"strings"
"text/scanner"
)
// ParseError is an error indicating invalid tag value
type ParseError interface {
error
// Source is a source name
Source() string
// Column is a column error occurred
Column() int
// Line is a line number error occurred
Line() int
}
type parseError struct {
message string
source string
column int
line int
}
func (e *parseError) Error() string {
return fmt.Sprintf("%s (%d:%d [%s])", e.message, e.line, e.column, e.source)
}
func (e *parseError) Source() string {
return e.source
}
func (e *parseError) Column() int {
return e.column
}
func (e *parseError) Line() int {
return e.line
}
type parser struct {
source string
s scanner.Scanner
}
func newParser(source string) *parser {
p := &parser{
source: source,
}
p.s.Mode = scanner.ScanIdents | scanner.ScanInts | scanner.ScanFloats | scanner.ScanStrings
return p
}
func (p *parser) Parse(tag string) ([]Definition, error) {
p.s.Init(strings.NewReader(tag))
result := []Definition{}
for {
tok := p.s.Scan()
switch tok {
case scanner.EOF:
return result, nil
case scanner.Ident:
ident := p.s.TokenText()
if p.s.Peek() == '=' {
p.s.Next()
value, err := p.parseValue()
if err != nil {
return nil, err
}
arg := map[string]interface{}{
ident: value,
}
result = append(result, newDefinition(ident, arg))
} else if p.s.Peek() == '(' {
p.s.Next()
arg, err := p.parseArgs()
if err != nil {
return nil, err
}
result = append(result, newDefinition(ident, arg))
} else if p.s.Peek() == scanner.EOF {
result = append(result, newDefinition(ident, map[string]interface{}{}))
}
case ',':
// NOP
default:
return nil, p.parseError(fmt.Sprintf("invalid token: %s", p.s.TokenText()))
}
}
}
func (p *parser) parseError(message string) error {
return &parseError{
message: message,
column: p.s.Position.Column,
line: p.s.Position.Line,
}
}
func (p *parser) parseValue() (interface{}, error) {
switch p.s.Peek() {
case '\'':
return p.parseString(p.s.Next())
case '[':
return p.parseArray(p.s.Next())
default:
tok := p.s.Scan()
switch tok {
case scanner.Ident:
return p.s.TokenText(), nil
case scanner.String, scanner.Int, scanner.Float:
if tok == scanner.String {
str := p.s.TokenText()
return str[1 : len(str)-1], nil
} else if tok == scanner.Int {
return strconv.ParseInt(p.s.TokenText(), 10, 64)
} else if tok == scanner.Float {
return strconv.ParseFloat(p.s.TokenText(), 64)
}
default:
fmt.Printf("%d, %s\n", tok, string(tok))
return nil, p.parseError(fmt.Sprintf("invalid value: %s", p.s.TokenText()))
}
}
return nil, p.parseError("invalid value")
}
func (p *parser) parseString(_ rune) (string, error) {
var buf bytes.Buffer
ch := p.s.Next()
for ch != '\'' {
if ch == '\n' || ch == '\r' || ch < 0 {
return "", p.parseError("unterminated string")
}
if ch == '\\' {
s, err := p.parseEscape(ch)
if err != nil {
return "", err
}
buf.WriteString(s)
} else {
buf.WriteRune(ch)
}
ch = p.s.Next()
}
return buf.String(), nil
}
func (p *parser) parseEscape(_ rune) (string, error) {
ch := p.s.Next()
switch ch {
case 'a':
return "\a", nil
case 'b':
return "\b", nil
case 'f':
return "\f", nil
case 'n':
return "\n", nil
case 'r':
return "\r", nil
case 't':
return "\t", nil
case 'v':
return "\v", nil
case '\\':
return "\\", nil
case '"':
return "\"", nil
case '\'':
return "'", nil
}
return "", p.parseError(fmt.Sprintf("invalid escape sequence: %s", string(ch)))
}
func (p *parser) parseArray(_ rune) ([]interface{}, error) {
result := []interface{}{}
for {
value, err := p.parseValue()
if err != nil {
return result, err
}
result = append(result, value)
next := p.s.Next()
if next == ']' {
return result, nil
}
if next == ',' {
continue
}
return result, p.parseError(fmt.Sprintf(", expected but got %s", string(next)))
}
}
func (p *parser) parseArgs() (map[string]interface{}, error) {
result := map[string]interface{}{}
for {
tok := p.s.Scan()
if tok != scanner.Ident {
return result, p.parseError(fmt.Sprintf("invalid attribute name: %s", p.s.TokenText()))
}
name := p.s.TokenText()
eq := p.s.Next()
if eq != '=' {
return result, p.parseError(fmt.Sprintf("= expected but got %s", string(eq)))
}
value, err := p.parseValue()
if err != nil {
return result, err
}
result[name] = value
next := p.s.Next()
if next == ')' {
return result, nil
}
if next == ',' {
continue
}
return result, p.parseError(fmt.Sprintf(") or , expected but got %s", string(next)))
}
}
// ParseTag parses a given tag value.
func ParseTag(value string, name string) ([]Definition, error) {
p := newParser(name)
return p.Parse(value)
}
// ParseStruct parses struct tags of given object. map key is a field name.
func ParseStruct(obj interface{}, tag string) (map[string][]Definition, error) {
result := map[string][]Definition{}
r := reflect.ValueOf(obj)
if r.Kind() == reflect.Ptr {
obj = r.Elem().Interface()
}
rv := reflect.TypeOf(obj)
for i := 0; i < rv.NumField(); i++ {
f := rv.Field(i)
value := f.Tag.Get(tag)
if len(value) == 0 {
continue
}
defs, err := ParseTag(value, rv.Name()+"."+f.Name)
if err != nil {
return nil, err
}
result[f.Name] = defs
}
return result, nil
}